Plasma device using coaxial waveguide, and substrate treatment method

ABSTRACT

Examples of a plasma device includes a coaxial waveguide having an inner conductor and an outer conductor enclosing the inner conductor with a first gap provided between the outer conductor and the inner conductor, the coaxial waveguide having a shape of branching at a plurality of branch parts, a plurality of rods having a conductor and a dielectric enclosing the conductor with a second gap provided between the dielectric and the conductor, the plurality of rods connecting two end parts of the coaxial waveguide branched at the branch parts, so as to connect the first gap and the second gap, and a conductive stub provided at a branched portion, obtained by branching at the branch parts, of the coaxial waveguide, the conductive stub being insertable to and removable from the first gap.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/872,135 filed on Jul. 9, 2019, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

Examples are described which relate to a plasma device using a coaxial waveguide and a substrate treatment method using the same.

BACKGROUND

As disclosed in WO2011/021607, in some plasma devices, a microwave is used as a plasma source. This plasma device has stub member that is extendible from an outer conductor side to an inner conductor side. The inner conductor is positionally displaced with respect to the center of the outer conductor and this makes the intensity of a microwave nonuniform due to nonuniform radial gaps between the inner conductor and outer conductor. The stub member is provided to relieve adverse effects due to the positional displacement.

There is a plasma device that has a different basic structure from that of WO2011/021607. Concretely, a coaxial waveguide having a branched shape is connected by a rod covered with a dielectric, and a microwave is provided from the coaxial waveguide into the dielectric. That is, the microwave introduced from a microwave introduction part of the coaxial waveguide is transmitted through a branch structure of the coaxial waveguide, and eventually reaches a plurality of rods. An electric field that is generated through the dielectrics of the rods causes plasma to be generated. Such a plasma device as generating plasma by using a plurality of rods cannot control the ratio of microwave power provided to the plurality of rods.

SUMMARY

Some examples described herein may address the above-described problems. Some examples described herein may provide a plasma device capable of controlling plasma distribution and a substrate treatment method.

In some examples, a plasma device includes a coaxial waveguide having an inner conductor and an outer conductor enclosing the inner conductor with a first gap provided between the outer conductor and the inner conductor, the coaxial waveguide having a shape of branching at a plurality of branch parts, a plurality of rods having a conductor and a dielectric enclosing the conductor with a second gap provided between the dielectric and the conductor, the plurality of rods connecting two end parts of the coaxial waveguide branched at the branch parts, so as to connect the first gap and the second gap, and a conductive stub provided at a branched portion, obtained by branching at the branch parts, of the coaxial waveguide, the conductive stub being insertable to and removable from the first gap.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 is a perspective view showing a configuration example of a plasma device;

FIG. 2A is a partial cross-sectional view of the plasma device;

FIG. 2B is a cross-sectional view of the coaxial waveguide;

FIG. 2C is a cross-sectional view of the rod;

FIG. 3 is a plan view of the plasma device;

FIG. 4 is a perspective view of the branch part;

FIG. 5 is a cross-sectional view of a part of the coaxial waveguide;

FIG. 6 illustrates stubs according to another example;

FIG. 7 illustrates stubs according to yet another example;

FIG. 8 is a plan view of the stubs;

FIG. 9 illustrates an arrangement example of stubs;

FIG. 10 is a graph showing a result of an electromagnetic field simulation;

FIG. 11 illustrates the electric field intensities of the rods;

FIG. 12 illustrates the electric field intensities of the rods; and

FIG. 13 illustrates the electric field intensities of the rods.

DETAILED DESCRIPTION

A plasma device and a substrate treatment method will be described with reference to drawings. The same reference signs may be used for the same or corresponding components, thereby omitting redundant descriptions.

FIG. 1 is a perspective view showing a configuration example of a plasma device. This plasma device includes a microwave introduction part 10. A coaxial waveguide 12 is connected to the microwave introduction part 10. A microwave is provided from the microwave generator outside the plasma device to the coaxial waveguide 12 via the microwave introduction part 10. A tuner 11 is provided in the vicinity of the microwave introduction part 10. The tuner 11 makes a reflected wave within the microwave introduction part 10 advance again to the coaxial waveguide 12.

The coaxial waveguide 12 includes an introduction waveguide 12A, a center waveguide 12B, and an edge waveguide 12C. The introduction waveguide 12A is a waveguide extending in the z direction. To this introduction waveguide 12A, the edge waveguide 12C branching from the introduction waveguide 12A in the x positive and negative directions is connected. The edge waveguide 12C branches from the introduction waveguide 12A at a branch part 12D, and subsequently branches again, thereby being connected to a side surface of a housing 14. The branch part 12D functions as a first branch part that causes a microwave introduced from the microwave introduction part 10 to the coaxial waveguide 12 to branch in three directions.

Another branch part is provided below the branch part 12D of the introduction waveguide 12A, and the center waveguide 12B branching in the x positive and negative directions is connected at the other branch part. The center waveguide 12B branches several times and then is connected to the side surface of the housing 14.

FIG. 1 illustrates that six end parts 12E of the coaxial waveguide 12 are connected to the left side of the housing 14. Also, to the right side of the housing 14, six end parts 12E of the coaxial waveguide 12 are connected. Thus, the coaxial waveguide 12 has the microwave introduction part 10 and the plurality of end parts 12E that is obtained by branching at a plurality of branch parts. A branch part nearest to the microwave introduction part 10 among the plurality of branch parts is a first branch part, that is, the branch part 12D. According to another example, the number of end parts can be increased or decreased by increasing or decreasing the number of branch parts of the coaxial waveguide 12. A chamber 16 is provided below the housing 14.

FIG. 2A is a partial cross-sectional view of a plasma device. This figure illustrates the cross section of the coaxial waveguide 12 and rods, where part of the device is omitted or simplified. The introduction waveguide 12A has an inner conductor 12 a′ and an outer conductor 12 a″ that encloses the inner conductor 12 a′ with a first gap 13 provided between the outer conductor 12 a″ and the inner conductor 12 a′. The center waveguide 12B has an inner conductor 12 b′ and an outer conductor 12 b″ that encloses the inner conductor 12 b′ with the first gap 13 provided between the outer conductor 12 b″ and the inner conductor 12 b′. The edge waveguide 12C also has an inner conductor and an outer conductor that encloses the inner conductor with the first gap provided between the outer conductor and the inner conductor. Thus, in this example, the whole of the coaxial waveguide 12 having a shape of branching at a plurality of branch parts has the inner conductor and outer conductor. The inner conductor, outer conductor, and housing 14 are of metal.

In FIG. 2A, a susceptor 26 provided in the chamber 16 is illustrated. On the susceptor 26, a substrate that is a processing object is mounted. According to one example, the susceptor 26 can be provided below a plurality of rods 24. Gas is provided into the chamber 16 from a gas source 27 according to processing contents. Gas in the chamber 16 can be exhausted, for example, through an exhaust port below the susceptor 26.

FIG. 2B is a cross-sectional view of the coaxial waveguide 12. Any part of the coaxial waveguide 12 has a first gap 13 between an inner conductor and annular outer conductor.

As shown in FIG. 2A, the rods 24 are provided inside the housing 14. Each of the rods 24 has a conductor 20 and a dielectric 22 that encloses the conductor 20 with a second gap 21 provided between the dielectric 22 and the conductor 20. Each of the rods 24 connect two end parts of the coaxial waveguide which has branched at a branch part, thereby connecting the first gap 13 and second gap 21.

FIG. 2C is a cross-sectional view of the rod 24. The material of the dielectric 22 can be, for example, ceramic such as alumina (Al₂O₃) or aluminum nitride (AlN).

FIG. 3 is a plan view of the plasma device. The rods 24 inside the housing 14 are indicated by dashed lines. The plurality of rods 24 are arranged substantially in parallel, being divided into center rods and two edge rods sandwiching the center rods. Concretely, four rods 24 in the center among six rods 24 are center rods that connect the center waveguides 12B with each other. Two rods 24 at both ends among six rods 24 are edge rods that connect the edge waveguides 12C with each other. In this example, all the rods 24 have the same configuration as the cross section exemplified in FIG. 2C.

The inner conductor of the coaxial waveguide 12 and the conductor of the rods 24 are not particularly limited as long as they are metals: for example, they are of silver-coated copper. The outer conductor of the coaxial waveguide 12 is also not particularly limited as long as it is a metal: for example, it is of aluminum.

In FIG. 3 , the outer edge of the susceptor 26 is drawn by an alternate long and short dash line. In this example, all of the rods 24 are located directly above the susceptor 26.

In the example shown in FIG. 1 , the center waveguide 12B branches two times both in the x positive and negative directions, thereby allowing four center rods to be provided. However, any number of center rods can be provided by changing the number of branch parts of the center waveguide 12B.

In the example shown in FIG. 1 , the edge waveguide 12C branches once both in the x positive and negative directions, thereby allowing two edge rods to be provided. However, any number of edge rods can be provided by changing the number of branch parts of the edge waveguide 12C.

FIG. 4 is a perspective view of the branch part 12D. The edge waveguide 12C includes an internal conductor 12 c′ and an outer conductor 12 c″. In FIG. 4 , the insides of the outer conductor 12 a″ and 12 c″ are visualized. Stubs 30 are provided at the branch part 12D that is the first branch part. The stubs 30 are formed, for example, of a conductor such as a metal. In an example in FIG. 4 , a plurality of columnar stubs 30 is illustrated. The stubs 30 can be inserted into the first gap 13 and removed from the first gap 13. The stubs 30 can be fitted into, for example, a hole of the outer conductor 12 a′ without a gap.

FIG. 5 is a cross-sectional view of a part of the coaxial waveguide 12 where the stubs 30 are provided. In an example in FIG. 5 , six stubs 30 are annularly provided. The number of stubs 30 may be one; though a plurality of stubs can be provided. The plurality of stubs 30 can enclose the inner conductor 12 a′ in plan view. The protrusion amount “d” of the stubs 30 in the direction of the inner conductor 12 a′ is defined by a distance between the position, nearest to the inner conductor 12 a′, of each of the stubs 30 and an inner wall of the outer conductor 12 a″.

The arrows in the x positive and negative directions in FIG. 4 indicate microwaves that are provided to the edge waveguide 12C. The arrow in the z negative directions in FIG. 4 indicates a microwave that is provided to the center waveguide 12B without being branched at branch part 12D. Thus, the branch part 12D causes a microwave power provided from the microwave introduction part 10 to branch into three directions. In addition, the branch part 12D that is the first branch part determines whether the microwave introduction part 10 is connected to the center rods or the microwave introduction part 10 is connected to the edge rods. The ratio between the microwave power to the center rods and the microwave power to the edge rods can be adjusted according to the protrusion amount d of the stubs 30 described above. A continuous change in the protrusion amount d of the stubs 30 causes a continuous change in the above ratio. Adjustment of the ratio between the microwave power to the center rods and the microwave power to the edge rods allows the plasma generation rate outside the rods to be controlled by the centers and edges. Thus, the protrusion amount d of the stubs is changed, thereby changing the plasma distribution.

FIG. 6 illustrates stubs according to another example. In this example, stubs 32 are prism-shaped. FIG. 7 illustrates stubs according to yet another example. In this example, two stubs 34 are provided. A surface of each of the stubs 34 that faces the inner conductor 12 a′ has the same shape as that of the surface of the inner conductor 12 a′. FIG. 8 is a plan view of the stubs 34 shown in FIG. 7 . The stubs 34 move in the arrow directions so as to change their protrusion amount. A surface 34A of each of the stubs 34, the surface 34A facing the inner conductor 12 a′, is made to have the same or similar shape as the surface shape of the inner conductor 12 a′, thereby allowing most of the first gap 13 to be closed by the stubs 34.

Thus, stubs of various shapes can be used. The shape of a stub can be freely set in consideration of, for example, the easiness of manufacture, the easiness of inserting into and removing from the first gap 13, the occluded area of the first gap 13, etc.

FIG. 9 illustrates an arrangement example of stubs. In this example, stubs 36 and 38, in addition to the stubs 30 described above, are provided to the edge waveguide 12C. The stubs 36 and 38 are inserted into and removed from the first gap 13 in the edge waveguide 12C. In this configuration example, the protrusion amount of the stubs 30, 36, and 38 toward the first gap 13 are adjusted, thereby allowing the distribution of plasma to be changed. According to further another example, it is possible to provide the stubs 36 and 38 and omit the stub 30.

In the above-described example, the configuration is made such that stubs are provided at the branch part 12D that is a first branch part when viewed from the microwave introduction part 10 and thereby the ratio of microwave power between the center rods and edge rods can be adjusted. However, stubs can be provided at an any branched portion, which is obtained by branching at a branch part, of the coaxial waveguide 12. For example, stubs can be provided at the second or third branch part when viewed from the microwave introduction part 10.

A substrate treatment method using the above-described plasma device will be described. For example, gas is provided into the chamber 16 from the gas source 27 illustrated in FIG. 2A. Plasma is generated in the chamber 16 either in a state where gas has been provided into the chamber 16 or while gas is being provided into the chamber 16. Concretely, the power of a microwave introduced from the microwave introduction part 10 is distributed by inserting stubs in a branch part of the coaxial waveguide 12, and then the microwave is provided into a space covered by the dielectrics 22 of the plurality of rods 24. Then, the microwave that has seeped out through the dielectrics 22 causes plasma to be generated outside the dielectrics 22. This plasma diffuses in the chamber 16, resulting in plasma generation in a space enclosed by the chamber 16 outside the dielectrics 22. By using the plasma, a substrate on the susceptor 26 is treated. Substrate treatment is, for example, film formation, etching, or film modification.

When the protrusion amount d of stubs is 0, the plasma uniformity is usually non-uniform. The degree of non-uniformity depends on process condition. Without inserting stub into first gap 13, there is a case that plasma is distributed non-uniformly which result in non-uniformity in the electric field intensities as illustrated in FIG. 10 . Stub can be used to control the ratio of power in this kind of a case and to adjust the plasma non-uniformity. When the stubs are made to protrude in the direction of the inner conductor from the inner wall of the outer conductor, the ratio of power distribution to the plurality of rods varies, thereby allowing the electric field intensities of the plurality of rods to be made non-uniform. Making the electric field intensities of rods non-uniform allows non-uniformity in a process, such as the non-uniformity in plasma density, to be compensated, thereby improving a process uniformity. In other words, a nonuniform plasma distribution can provide a process uniformity. In order to achieve such an objective as described above, the electric field intensities of center rods can be made higher than the electric field intensities of edge rods, and also the electric field intensities of center rods can be made lower than the electric field intensities of edge rods.

FIG. 10 is a graph showing a result of an electromagnetic field simulation. The horizontal axis represents the protrusion amount d of a stub and the vertical axis represents the ratio of power absorption amount between center rods and edge rods. As a model for the simulation, the above described plasma device under a relatively simple condition is adopted where it is assumed that the plasma density inside the chamber 16 is uniform. As the structure of stubs, the stubs 34 shown in FIG. 7 are adopted for calculation. This simulation is performed for the case where the plasma density, that is, the electron density is 5.00E+17 (l/m³) and for the case where the plasma density is 7.00E+17 (l/m³).

In this simulation, a tendency is seen for both the plasma densities that the power absorption amount at the center rods becomes more as the stub protrusion amount becomes more. More concretely, the stub protrusion amount is gradually increased, thereby allowing a state where the power absorption amount of the edge rods is more than that of the center rods to be shifted to a state where the power absorption amount of the edge rods is less than that of the center rods. Therefore, when an initial process result indicates that “the plasma density at the edges is high,” the stub protrusion amount is increased so as to increase the power absorption amount of the center rods, thereby allowing plasma to be substantially uniform. The inventor has confirmed that the same tendency as this can be obtained with the stub shapes shown in FIGS. 4 and 6 . FIGS. 11 to 13 illustrate the electric field intensities of the rods when the stub protrusion amount is changed. As for the rods, a dark blue part has a lower electric field intensity than a red part. An area colored with red has the highest electric field intensity, and an area colored with dark blue has the lowest electric field intensity.

The plasma device and substrate treatment method described above can be modified in various forms. For example, means for inserting and removing the stubs to and from the branch part in the coaxial waveguide may be a manual operation, electronic control, or a screw operation. In inserting and removing the stubs by a manual operation, the stub protrusion amount can be correctly grasped by having scales provided at a side surface of the stubs. For the case of screw-type stubs, the stub protrusion amount can be correctly grasped by the screw rotation amount. 

The invention claimed is:
 1. A plasma device, comprising: a coaxial waveguide having an inner conductor and an outer conductor enclosing the inner conductor with a first gap provided between the outer conductor and the inner conductor, the coaxial waveguide having a shape of branching at a plurality of branch parts; a plurality of rods having a conductor and a dielectric enclosing the conductor with a second gap provided between the dielectric and the conductor, the plurality of rods connecting two end parts of the coaxial waveguide branched at the branch parts, so as to connect the first gap and the second gap; a conductive stub provided at a branched portion, obtained by branching at the branch parts, of the coaxial waveguide, the conductive stub being insertable to and removable from the first gap; and wherein the coaxial waveguide comprises a microwave introduction part and a plurality of end parts, the plurality of end parts being obtained by branching at the plurality of branch parts; and the stub is provided at a first branch part, the first branch part being a branch part nearest to the microwave introduction part among the plurality of branch parts.
 2. The plasma device according to claim 1, wherein the first branch part causes a microwave introduced from the microwave introduction part to the coaxial waveguide to branch in three directions.
 3. The plasma device according to claim 1, wherein the plurality of rods is arranged substantially in parallel, being divided into center rods and two edge rods sandwiching the center rods; and the first branch part is a branch part determining whether the microwave introduction part is connected to the center rods or the microwave introduction part is connected to the edge rods.
 4. The plasma device according to claim 1, comprising a susceptor provided below the plurality of rods.
 5. The plasma device according to claim 1, wherein the stub is provided in plurality.
 6. The plasma device according to claim 1, wherein a plurality of the stubs encloses the inner conductor in plan view.
 7. The plasma device according to claim 1, wherein the stub is column-shaped or prism-shaped.
 8. The plasma device according to claim 1, wherein a surface of the stub that faces the inner conductor has the same shape as the surface shape of the inner conductor. 